Alright, I'm bored and I'm waiting for my rice to cook so I can eat lunch. Everything I say should be taken with a grain of salt. I'm not exactly the most knowledgeable person about this game.
I play with a friend all the time and occasionally with another friend. I leveled apprentice and my other friends play huntress. We for the most part have tried to progress one level at a time going through all difficulties. We are at max level and I've gone a 40/70/40/70 tower build and my friend has gone something like a 50/70/40/50 trap build.
After much trial and error, I can say for the most part that the magic missile tower is worthless. On Insane difficulty which is the one we play on most, or at least have the most difficulty with, the huge number of mobs streaming at you just scream for aoe defenses. Magic missile turret does not provide this. On the plus side, it's non-elemental.
Moving on, the fireball turret at first glance seems awesome but sadly after closer inspection you'll notice that for mobs to take full damage from it, it needs to hit dead on. For some reason I've seen mobs surrounding the targeted mob only taking partial damage.
The lightning turret is good in certain ways... Usually I use it to take care of mobs that somehow get past my friend's trap stacking and my wall or to take out aerial units that bypass the defenses. Summoners are usually a problem for a lot of people and while the chaining ability of the tower allows it to hit the ones standing in the back the damage is too low to actually finish them usually so they just get healed. Also, the stun doesn't work on ogres/bosses so you're better off using a fireball tower for more damage.
The deadly striker is....anti-air. For some reason in the coding it actively likes taking out wyverns. If, and I stress if here, you can set it up to fire only at say an ogre/or boss, it works fairly well, but if that target is mixed in with other mobs it's just as likely to go one shot a club wielding goblin than hit the high hp mob. Also, they're quite expensive in defense units.
Oh, I forgot to mention the magic blockade. Awesome enough in it's own way. It will remove the elemental immunity of any mob that hits it. It also only costs one defense unit. An amazing wall for it's cost it does however have around 1.8k less hp than an equivalent squire blockade, but that's cause you can build 3 of them for the same DU. I won't complain about that aspect. What I will complain about is the fact that all too often kobold archers will just shoot over them to hit either the tower behind it or the crystal itself.
Alright, enough about the towers. After a lot of playing and testing my friend and I came to the conclusion that on insane difficulty it's much better to use just my wall and his traps than my wall and towers. I should clarify this by saying the reason isn't so much the damage but the defense units. If I try to hold with just my wall and some combination of towers it inevitably costs more in defense units that it would to just use my 1 point wall and a proximity trap. (Which by the way, does non-elemental damage) The plus side of this is that those freed up defense points usually go towards me building more deadly strikers. These are invariably used for anti-air, to pick off ranged mobs that refuse to step on his traps, or placed in advance to deal with an ogre/boss that we know is coming. All in all for the most part as a tower apprentice duoing with a trap huntress I'm relegated to for the most part just using my cheap wall and my deadly strikers. Other than that I run around repairing and occasionally using mana bomb or help hold a location. In the end I'm somewhat disappointed that I don't get more utility out of the majority of my towers.
I know it's long, but that's about the sum of all the knowledge I've picked up playing tower apprentice to 70. I can't say much about the hero build since I've never tried it in hopes that apprentice tower build will get buffed someday, but for the most part aoe wise other classes can do a better job than you.
Now that I've shared my knowledge I hope you actually gain something from it and make an informed opinion rather than an impulse decision.
Edit: I should clarify it a little. Basically the damage output is too low on the apprentice's aoe towers so in order to do the same thing as another class you end up having to drop more towers to achieve the same effect which costs more DU. Which on insane you can't afford to do since every defense unit counts. Especially when you can't stand around healing your defenses when you need to be distracting/damaging an ogre/boss. (Or getting harassed by those leaping elves...)